The invention pertains to a tracked vehicle with a drive system which performs driving, braking, directional change, and steering functions as a function of corresponding control commands from an electronic control unit.
A tracked vehicle of this type for use on ski slopes is generally known through similar ski slope vehicles of the applicant. The chassis of a known tracked vehicle of this type has a left side and a right side, each of which has its own chain drive. Each chain drive is driven by a hydraulic drive system, which has a hydraulic pump unit on each side of the chassis. The two hydraulic pump units are driven by an internal combustion engine, which acts by way of a power divider. The engine can be either a diesel or a spark-ignition engine. Each chain drive has at least one drive wheel, which is driven by a hydraulic motor, which motor is part of the hydraulic drive system. Steering operations, accelerations and decelerations, and changes of driving direction by switching between forward and reverse are carried out by appropriate actuation of the hydraulic motors for the chain drives on the two sides of the vehicle in different ways. By actuating the chain drives on the left and right side differently, it is possible to steer the vehicle. The hydraulic motors are actuated by appropriate hydraulic control means, which are operated in turn by a central electronic control unit.
The task of the invention is to create a tracked vehicle of the type indicated above which makes it possible to control the tracked vehicle even after the electronic control unit has failed or malfunctioned.
This task is accomplished by the provision of at least one separate brake system which operates without current and which can be enabled by at least one actuating element, which acts in the absence of current, when a function parameter of the drive system exceeds or falls below at least one limit value. The brake system ensures that, even in the case of an electronic failure, an electronic shut-off, or an electronic malfunction, it is still possible for the driver to control the vehicle and in particular to brake it to a stop. If the drive system of the tracked vehicle has a hydraulic drive, the pressure in the corresponding hydraulic circuit is especially suitable as the function parameter. Depending on the purpose, it is possible to define one or more pressure limits, above or below which the brake system is automatically enabled by appropriate automatic actuation. A suitable actuating element for a hydraulic system is a hydraulic valve which switches from one state to another as a function of pressure.
In an elaboration of the invention, the brake system has at least one function-monitoring means. Because the separate brake system may possibly never be used during normal operation of the tracked vehicle, a failure of this brake system would not necessarily be noticed. Thus the function-monitoring means are provided, which ensure that, when the variable in question exceeds or falls below the selected limit, the brake system will function reliably. The brake system preferably has brake devices on both sides of the vehicle, and these brake devices can be actuated in different ways so that steering operations can also be performed.
As a further elaboration of the invention, the minimum of one actuating element can switch the brake system from its rest mode to a steering function mode or to a braking function mode when the function parameter exceeds or falls below one or another limit. Especially for the sake of the steering function, the brake system must be able to actuate the two sides of the tracked vehicle in different ways. For this purpose, a separate brake device is preferably assigned to each side of the vehicle. The braking function mode is required especially in cases where the braking force which can be provided by the similar braking function of the drive system is not sufficient in and of itself to decelerate the vehicle to the extent intended by the driver of the vehicle when he pushes down forcefully on the brake pedal and thus produces a strong braking pressure. A steering function mode is necessary especially for cases in which the electronic circuitry of the vehicle fails, because otherwise it would not be possible to control the vehicle.
As a further elaboration of the invention in which the electronic control unit can actuate the drive system to perform steering functions by electronically converting control movements of a manually operated controller, the manual controller has a mechanical connecting element, which, upon the failure of the electronic control unit, can be enabled by an automatic actuator to establish the control connection between the manual controller and the drive system and/or the separate brake system. Because the control commands are transmitted from the manual controller to the drive system by purely electronic means in this design, it must be guaranteed that the tracked vehicle can still be controlled even after the failure of the electronic circuitry. The provision of a mechanical connection, which can be enabled when needed, between the manually operated controller and the drive system or the separate brake system means that the tracked vehicle can be steered under any conditions.
As a further elaboration of the invention, a brake device which is fed by at least one separate energy-supply circuit and which is thus independent of the hydraulic drive system is assigned to each side of the chassis as part of the brake system. The manual controller is connected mechanically to at least one actuating element of the energy supply circuit. When the electronic control unit fails, this actuating element is enabled by an automatic actuator, which operates in the absence of current. The actuating element can thus proceed to actuate the brake devices on both sides as a function of corresponding steering movements of the manual controller. The energy supply circuit for the brake device in question, which is independent of the hydraulic drive system, can be electrical, pneumatic, or hydraulic. Of course, the brake devices themselves can also be integrated electrically, pneumatically, or hydraulically into the system in a corresponding manner. The solution according to the invention guarantees that, even after the electronic circuitry fails or is turned off or malfunctions, it still remains possible to steer the vehicle at least until it can be brought to a stop. As a result of this feature, which is especially relevant in terms of safety, it becomes possible for the tracked vehicle to be approved for highway operation in spite of the purely electronic control of its travel direction.
As a further elaboration of the invention, a hydraulic circuit is provided as the energy supply circuit. This circuit is fed by a pump device, which is connected mechanically to at least one side of the vehicle in such a way that the coasting of the tracked vehicle can supply the pump device with sufficient feed pressure. This ensures that there will always be sufficient feed pressure available to actuate the brake system. The mechanical connection between the minimum of one pump device and components which rotate when the vehicle is coasting means that the pump device will continue to operate under these conditions and that the necessary feed pressure can be maintained, provided that the minimum of one pump device is designed properly to work with the brake system.
As a further elaboration of the invention, an automatic pressure control valve, which actuates the two hydraulic circuits and the associated brake devices in a manner proportional to the steering movements of the manual controller, is used as the actuating element. When the vehicle is traveling straight ahead, the pressures in the two hydraulic circuits will be kept equal. When a steering movement is made, the pressure in one of the hydraulic circuits will become lower than that in the other circuit. The desired brake device will thus execute the corresponding braking function, as a result of which the speed of the chain drive in question is reduced as intended.
As a further elaboration of the invention, each brake device has a mechanical brake, especially a multi-disk brake, which acts on the sprocket wheel on the side of the chassis in question. This is a design which offers an especially high degree of functional reliability and also allows the transmission of high braking forces.
As a further elaboration of the invention, a double-acting multi-disk brake is provided. This multi-disk brake is preferably provided with two brake pistons or brake disks, which can be actuated independently of each other and each of which acts on a corresponding stack of plates.
As a further elaboration of the invention, at least one pressure sensor is integrated into the minimum of one energy supply circuit of the minimum of one brake device to monitor the function of the device. This pressure sensor is connected to the electronic control unit. A hydraulic circuit is provided as the energy supply component in this design.
As a further elaboration of the invention, at least one actuating element which switches from one state to another as a function of pressure is assigned to the minimum of one energy supply circuit, and a position sensor is assigned to the automatic actuating element. These two function-monitoring components are connected to the electronic control unit and make it possible to monitor the operational status of the brake system.